Include published date field

[keegansmith21]

Added the published_date field to the book_products and export_book_product_list tables. For the latter, this takes the place of the time_field that is no longer in use.

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (1f32f8f) 95.19% compared to head (0c7fedf) 95.19%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #185 +/- ## ======================================== Coverage 95.19% 95.19% ======================================== Files 16 16 Lines 2392 2392 Branches 311 311 ======================================== Hits 2277 2277 Misses 71 71 Partials 44 44 ```

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[kathrynnapier]

Noting that @kathrynnapier and @bechandcock will do a sprint through current BAD dashboards to remove any (erroneous) inclusions of time_field in visualisations/filters (not a required field, but a hangover from previous kibana visualisations)

[keegansmith21]

Thanks Keegan, looks good!

Would it make sense to make the descriptions consistent between oaebu_workflows/database/schema/book_product.json and oaebu_workflows/database/schema/oaebu_publisher_book_product_list.json ?

e.g. "The date the book was published" vs "The date of publication of the book"

This could be addressed later as a future improvement if there are more inconsistencies between the two schemas.

Thanks Kathryn! There are probably quite a lot of these little inconsistencies between the schemas. But I do agree that it's better to try to keep them all the same. I'll change it here and perhaps we can address this issue with the upcoming refactor.